This invention relates to a method for the preparation of p-fluoroaniline.
Parafluoroaniline is a commercially available compound, useful as a chemical intermediate in the preparation of dyestuffs, pesticides and pharmaceuticals.
The use of p-fluoroaniline as a starting material for the preparation of pharmaceuticals (anti-inflammatory compounds) is described in U.S. Pat. Nos. 3,681,445 and 3,692,821.
Prior art methods for the preparation of p-fluoroaniline include the following: U.S. Pat. Nos. 2,198,249; 2,884,458; 3,639,482 and 3,558,707 disclose the preparation of p-fluoroaniline by catalytic hydrogenation of nitrobenzene. U.S. Pat. No. 3,910,985 teaches the conversion of nitrobenzenes to 4-fluoroanilines by treatment with hydrogen and hydrogen fluoride. U.S. Pat. No. 4,145,364 disclose the preparation of p-fluoroaniline by treatment of phenylazide with hydrogen fluoride.
It has also been disclosed in the chemical literature that moderate yields of p-fluoroaniline may be achieved by the low temperature reaction of anhydrous hydrogen fluoride with N-phenylhydroxylamine. See Patrick et al, J. Organic Chemistry 39 (12), 1758 (1974); and Titov et al, Zhur Obshchei. Khim., 23, 346 (1953). Other investigators have suggested a mechanism for the reaction wherein p-fluoroaniline is prepared by catalytic reduction of nitrobenzene in anhydrous hydrogen fluoride. The suggested mechanism, according to Fieller et al, J. Org. Chem 26, 4014 (1961), involves the reduction of nitrobenzene to N-phenylhydroxylamine followed by the in-situ rearrangement of the latter in hydrogen fluoride.
Although p-fluoroaniline may be produced by various prior art processes, such processes are typically characterized by low yields, unwanted by-products, and/or uneconomical process conditions. It will be appreciated that further improvements in the efficiency and economy of preparation and yield and purity of the desired product, p-fluoroaniline are desirable.